Such a crappy product. In Vancouver I see tile guys nailing down 1/2" OSB as tile prep. That's all it takes to make local building code. Just looked at a kitchen grout job that failed totally. All the grout is falling out.

Floor heat works. Grout is gone. So is the tile installer. And if push comes to shove the tile guy set the tile by the book....

Not all osb is created equal. At least a couple of brands available in the USA have a many year warranty against it delaminating along with a good warranty on the open build time before the building is closed up. They are flatter, and more stable than ply, and for the same sized panel, Advantech is about 10% stiffer that the ply it may be replacing, which helps between joist deflection. Advantech is actually made with alternating layers of the wafers, around 20 or so in the 3/4" product if I remember correctly, which is why it is stiffer than the equivalent ply. Glued to the joists and ring-shank or proper screws, and it makes a very solid floor.

Some of it is crap, but not all. Waferboard, on the other hand, is pretty much crap, regardless of who makes it (made with random, or non-oriented wafers pressed together with glue).

So are you saying the advantech is a good choice for subflooring under tile?

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It depends on what you are using as a decoupling layer. Some thinset manufacturers do not approve their products over any osb...they do not make exceptions, some do. Schluter allows it under Ditra, and some cbu manufacturers don't have a restriction. I've not had issues using it, but you might depending on how much traffic it gets before you're ready to tile...it has a coating on it that can affect the thinset bond, depending on the type you use. With my installs, there was a bunch of work done in the room before it got ready to tile, so that coating was worn off, and stuff stuck REALLY well. I was mixing some SLC up, and doing it in one area with some Advantech. There was no primer on that area, but I ended up getting some drips of SLC on the subfloor. When I tried to clean it up (after it had cured), I tried to pry it off with a putty knife, a chisel, and to just bang on it with a hammer, and the only way I was able to get it to come off was to grind it off the Advantech. Do that same thing on virgin material, and it probably would have come off easier.

So, it's a qualified yes, depending on what and how you plan to install it. Personally, I like it because it is so flat, and the T&G is self-spacing (getting the T&G of regular ply to mate can be a pain sometimes). Screws are a pain to get into it, but if you're using construction adhesive like you should be on the joists, once that sets, you could pretty much take the fasteners out - the adhesive will hold it in place. I generally use construction adhesive and ring-shanked nails into the joists for the first layer, screws for the second, if there is one.

The first layer must be at least 5/8", and 3/4" is better since it holds screws better if you're adding a second layer, but the minimum called out in the TCNA guidelines is 15/32" - up to a point, more is better. That guideline calls for the ply to be exposure 1 or exterior rated glue and have no face lower than 'C'. It's harder to find suitable thin stuff, but it is available. When using a second layer of ply for natural stone, that second layer needs to be installed properly. The major reason for the second layer is to bridge the joints on the first. Where two ends meet on a joist, when there's deflection between the joists, those ends act like levers, pushing up. By installing the second layer offset (1/4-span), those ends in the first layer are supported better, preventing the jacking and the screw bond between the sheets aids the between joist deflection as well.

The first layer must be at least 5/8", and 3/4" is better since it holds screws better if you're adding a second layer, but the minimum called out in the TCNA guidelines is 3/8" - up to a point, more is better. That guideline calls for the ply to be exposure 1 or exterior rated glue and have no face lower than 'C'. It's harder to find suitable thin stuff, but it is available. When using a second layer of ply for natural stone, that second layer needs to be installed properly. The major reason for the second layer is to bridge the joints on the first. Where two ends meet on a joist, when there's deflection between the joists, those ends act like levers, pushing up. By installing the second layer offset (1/4-span), those ends in the first layer are supported better, preventing the jacking and the screw bond between the sheets aids the between joist deflection as well.

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OK Jim - awesome cut and paste info.

Keep the second layer no thinner than 5/8".

Who knows if construction adhesive expands while curing? Why would I write that? What implications does this have on your sub floor prep? Thin plywood over a subfloor as tile prep can actually make the floor worse than when you started.....

Keep the second layer no thinner than 5/8".

If you want 1/2" - use Wonderboard Lite 1/2"

If you need 3/8" - use Wonderboard Lite 1/4" and a medium bed thin-set.

And these cement board sheets get installed with thin-set under them and nailed off.

John Whipple is a 'more is better' kind of guy. The TCNA sets the industry guidelines AND tests the assemblies to verify that they work, and works just fine. Should you have some extenuating circumstances, then decide if more is better.